Treatment of magnesium and magnesium base alloys to increase their resistance to corrosion



Patented June 20, 1950 I s r; i:

Y TREATMENT oEIMAGNEs iI-iM AND MAGNEQ. I I

SIUM BASE ALLOYS TO INCREASE THE R a ans srauos 'ro oonno v p Rene GidegNewY k'N Y I NoDrawing. ,Applicatio Jul The invention relates to the treatmentot metal articles to increase their resistance toflcorrosmn'. It has special application to'the' treatment ,of

magnesium and its alloys to .'form a corrosion .re

sistant coating for such metals'but is useful also in the treatment of other metals and alloys.

It is an object of .my invention top'rovideflan improved method of treating metals and metal articles to increase their resistance 'to corrosion.

In my, copending application Serial No. 608,841, filed August 3, 1945, now U. vS. Patent" No. 12 165343, I'have disclosed that improvedresistance to corrosion of metals, for'example, magnesium, aluminum and iron, and alloys in which these metals form the principal ingredient, can

be obtained by treating in a boiling solution'com prising about 1 to 6% of potassium ,permanga nate and about 0.1 to 1% of a salt of a metal which is lower in the electromotive series thanthe metalto be protected; and furtherthat the protective value ofthe coating thereby, produced can be further enhanced or the stability-offthe coating increased by a subsequent treatmentwhich consists in dipping the articles in. fuming oil. In my copending application aforesaid I have disclosed further that an especially effective coating can be produced by-treatin g successively in two boiling solutions, each of which comprises about 1 to 6% of potassium permanganate, the first solution containing also a sulphate, such as a sulp'hateof aluminum, manganese or-zinc,.andthe second containing in addition to the perman-- ganate a salt of a metal which is lower-in the,

electromotive series than the metal which is being treated.

1' have discovered that a substantial additional improvement in corrosion resistance. of metals, for example, magnesium, aluminum and iron, and: alloys in which these metals form the principal:

ingredient, can be obtained by treating them,be-

fore immersion in the boiling potassium perman-= ganate solution, in a solution comprising about 0 .1 to 1% of a salt of a metal which is lower in the electromotive series than the metal to Joe-protected. This preliminary treatment may be performed at room temperature, but I prefer that it be performed at the boiling temperature.

Thus my present improved treatment in its preferred form comprises two principal steps;

first, atreatment in a solution comprising 0.1 to

1 of a salt ofthe class described (without the use of potassium permanganate), and 'secondga treatment in a solution at approximately boiling; temperature comprising about 1 to 6% of potasf' sium permanganate. In the secondstep there i may be added to the permanganate solution. about 0.1 to 1 of the same salt that was. used in the first solution, or at least one salt of a metal which is lower in the electromotive series than the metal which is being treated,

yin, 1e45,

-- feetive-results can beobtained when a salt'of the oi a r'netallowerjinthe electromotive series than group comprising zirconium, thorium, titanium tieriunyis used for thepreliininary treatment orisadded'tothe potassium permanganate in the second stepbftheprocess. In the case of treatmentsf of magnesium and aluminum, excellent res'iiltsar'e'obtained also with the use of manganese"sulphate"f'or the preliminarytreatment with the addition of aluminum sulphateto the potasshim permanganate or the sodium or potassium dichro'rnate in theboiling treatment.

The' percentages of the components of the boiling solutions' are pi importance in achieving op-\ t m .l,

"My mpro'v'ed treatment preferably is'preceded by clean ingtheIsurfaceof the metal article to be protected; This may be accomplished mechanically, Q-chemically, or electrochemically according sults.

tofwell know'n'methods which formno part of the;

presentinvention. However, by way ofexample, removalof th'e oxides'on the surface of magnesiiiin and. its alloys can be carried out by immersion in a .5 per cent chromicacidfsolution.

'In' some cases it is beneficial to. follow the I cleaningstep just'described withan electrolytic degreasing step v in which the work is made cathodelin' a' suitabIesoIutiOn. Such treatments are well known in the art, and these known treat-,

merits; finay omittei, I

I, In the principaltreating steps of my method I immerse them'et'al or metal articles to'be treated a solutiorgpreferably at boiling temperature, whicjhgas' Ihavef'stated, comprises about 0.1 to

befpracticed as desired, or may be 1% of, a {salt or salts o f'ja metal which is lower in the felectromotive series "than the metal being treated! :Tliereafter I immerse the articles in a solution, at approximately boiling temperature, comprising for example, potassium permangahate wit in the limits'stated and, a Saltor salts the metal being treatedfalso within the limits stated. It may be preferable'touse in the first solution a salt of a metal which is just slightly lowerdnthe .electromotive series than the metal ate aeaaed'anq tense. in the second solution a salt'pf a. metalwhich is lower in the electromotive series thantheametal of the salt used in the firstsolution, For example, assuming that t metalito be protected is magnesium, the first solution contain aluminum sulphate and the second, a water-soluble zinc salt. However a. salt such as Zr(SO4)2-ZrOSO3-2H2O is eifective for 7 use in both the first and second solutions. It

essential in all cases that the metal be treated in at least one solution comprising at 581th! a. metal lower in the electromotive series (ti-repreliminary solution) and that it be subsequentlymersed for a period of 30 minutes in a boiling treated in a boiling potassium permanganate solution (or solution of other highly oxidizing alkali metal salt) alone or in combination with a salt or salts of a metal lower in the series.

As also disclosed in my copending application aforesaid, other constituents can be added to the treating solution as may be desired for special purposes, for example, to impart. a particular color or texture to. the. protective coating or otherwise to vary its appearance or character in respects which do not substantially alter its corrosion resistant properties. amounts of selenicv acid may be employed in the treatment of magnesium by either the single solution method or the two solution method Ihave described. I have found that selenic acid, when added in small amounts up to about 0.05 per cent, imparts a dark reddish or mahogany color and gives a very smooth surface. In th two solution method, the selenic acid would be added to the second of the two solutions described.

The salt of the metal which is lower in the electromotive series than the. metal to be protected preferably is a sulphate, although acetatesmay also be used.

Treatment in thefirst. solution may becontinnod for a period of. to minutes or longer. Treatment in the second solution may be on the order of minutes or longer. However as the solutions used do not cause any appreciable dimensional change, the time of treatment can be extended as desired. The metal may be, washed between successive immersi'ons but that is not. necessary. At the conclusion of the treatment, the articles are washed in hot Water and allowed to dry. If desired, they are, then dipped in fuming oil, for example, in refined corn oil, for a period of a few seconds to on minute. During, this treatment some evolution of gas will be ob served, and at such time at this evolution ceases, the treatment can be terminated.

Finally, the articles are washed; in hot. soapy water and allowed to dry, or de-oiling can be performed by immersing in a boiling aqueous solution containing 2%v potassium permanganate and 0.1% of a sulphate such as aluminum or zinc, sulphates. In the case of magnesium alloys. the coating varies in col-or from black to gray or maroon, according to the particular alloy treated.

The coating grows blacker as the percentag of aluminum in the alloy increases. Thus a magnesium alloy which does not contain aluminum. takes a maroon color while a, magnesium alloy For example, small k containing 9% of aluminum takes a dark gray to I black color.

The coatings produced by the treatments I. have described are very adherent and can be brushed heavily with a, hard bristle brush Without any apparent-harm to the coatings.

Example 1 aqueous solution containing 6% potassium permanganate. Upon removal from the second solution the specimen was dipped in fuming refined corn oil and then washed. The specimen, when dried, had a brownish-black color.

Example 2 Example 3 A specimenof rolled sheet of magnesium alloy of the same composition given in Example 1 was treated as follows? It was cleaned and then immersed for a periodof 15 minutes in an aqueous solution, at boiling temperature, comprising 0.1% zirconium sulphate. After removal from this solution, the sheet was then immersed for a period of 40 minutes in aboiling aqueous solution containing 6% potassium-dichromate and 0.6% zirconium sulphate. Upon' removal from the second solution'the specimen was washed and allowed to dry: The coating was very smooth and of an even satin black color.

Example 4 A-specimen of rolled sheet of an aluminum alloy containing about 7 .0 silicon, 0.3% magnesium, balance substantially-aluminum plus usual impurities, was treated as follows: Immersed for a period of 1-5- minutes ina 1% boiling aqueous solution of Zr(-SO4)z-ZrOSO3-2H2O at room temperature. Thereafter it was immersed for a period ofi 45 minutes ina boiling solution contain 6% potassium permanganate and 0.6% 251163049 2: ZTOSOEF2H20. These treatments were followed by dipping thespecimen in fuming vegetable oil for 5 minutes, after which the specimen was Washed inhot-water to remove the oil film. The coating obtained was black. The treated sheet was tested byim-mersi-on in a 20% sodium chloride solution. for 300. hours, after which no Sign. of, corrosion was to. be observed.

Example 5 A. specimen.- of sheet steel containing about 0.28 to.0.33% carbon;,,0.40:to-0.60 manganese and 0.80 to, 1.1%. chromium, balance substantially iron plus usual. impurities, wa cleaned and immersed for a. periodof 10 minutes in a boiling aqueous solution, comprising 0.1% cerium sulphate. After removal from this solution the sheet was then immersed for a period of 30 minutes in a boiling aqueous solution containing 6% potassium per-.

manganate and 0.6 cerium sulphate. Upon removal from theisecondsolution, the specimen was dipped in fuming3oiland'then cleaned. The coating produced was" tough and. adherent. The

color would be described a black or brownish black.

It will be appreciated from the preceding description and examples that my improved treatment is extremely simple in character and can be practiced without the use ofspecial equipment. Moreover, it requires only a short time to produce an effective coating of smooth and pleasing appearance, the color of which can be varied. Another advantage of my treatment is that it is carried out without the use of acids or other substances which are dangerous to handle. The treatment is applicable to sheet, castings or articles made of dissimilar metals.

The terms and expressions which I have employed are used in a descriptive and not a limiting sense, and I have no intention of excluding such equivalents of the invention described, or of portions thereof, as fall within the purview of the claims.

I claim: 1. The 'methodpf treating magnesium and magnesium base alloy articles, which comprises immersing the articles in an aqueous solution in which the solute consists of about 0.1 to 1% of a sulphate of a metal which is below magnesium in the electromotive series, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature comprising about 0.1 to 1% of a salt of a metal which is be- Q low magnesium in the electromotive series and about 1 to 6% of potassium permanganate, said solutions being adapted to increase the resistance of said articles to corrosion.

2. The method of treating magnesium and magnesium base alloy articles, which comprises immersing the articles in an aqueous solution in which the solute consists of about 0.1 to 1% of a salt of a metal which is below magnesium in the electromotive series, and thereafter immers ing the articles in a boiling aqueous solution comprising about 0.1 to 1% of a salt of a metal which is below magnesium in the electromotive series and about 1 to 6% of potassium permanganate, said solutions being adapted to increase the resistance of said articles to corrosion.

3. The method of treating magnesium and magnesium base alloy articles, which comprises immersing the articles in an aqueous solution at approximately room temperature consisting of about 0.1 to 1% of manganese sulphate, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature comprising about 1 to 6% of potassium permanganate, said solutions being adapted to increase the resistance of said articles to corrosion.

4. The method of treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution at approximately room temperature consisting of about 0.1 to 1% of manganese sulphate, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature comprising about 0.1 to 1% of a salt of a metal which is lower in the electromotive series than the metal to be protected and about 1 to 6% of potassium permanganate and which is effective to increase resistance to corrosion.

5. The method of treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution in which the solute consists of about 0.1 to 1% of a salt of a metal which is below magnesium in the Cir electromotive series, and thereafter immersing the articles ina boiling aqueoussolution in which the solute comprises primarily about 1 to 6% of potassium permanganate, said solutions being effective to increase the resistance of said articles to corrosion.

. 6. The method of treating magnesium and magnesiumbase :alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution at approximately room temperature consisting of about 0.1 to 1% of at least one salt selected from the group consisting of zirconium, thorium, titanium and cerium, and thereafter immersing the articles in :an aqueous solution at approximately boiling temperature in which the solute comprises primarily about 1 to 6% of potassium permanganate, said solutions being effective to increase the resistance-of said articles to corrosion.

7. The method of. treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution consisting of about 0.1 to 1% of. at least one salt selected from the group consisting of zirconium, thorium, titanium and cerium, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature in which the solute consists of about 0.1 to 1% of a salt of a metal selected from a group comprising zirconium, thorium, titanium and cerium and about 1 to 6% of potassium permanganate, said solution being effective to increase the resistance of said articles to corrosion.

8. The method of treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution at approximately room temperature in which the solute consists of about 0.1 to 1% of a zirconium salt, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature in which the solute comprises primarily about 1 to 6% of potassium permanganate, said solutions being effective to increase the resistance of said articles to corrosion.

9. The method of treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution at approximately room temperature in which the solute consists of about 0.1 to 1% of a zirconium salt, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature in which the solute comprises primarily about 0.1 to 1% of a zirconium salt and about 1 to 6% of potassium permanganate, said solutlons being effective to increase the resistance of said articles to corrosion.

10. The method of treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises immersing the articles in an aqueous solution at approximately room temperature in which the solute consists of about 0.1 to 1% of Zr (S04)! ZrOSOa -2H2O and thereafter immersing the articles in an resistance to corrosion, which comprises iiiimersing the articles in an aqueoussol-ution at approximately room temperature in which the solute consists of about 0.1 to 1% of ZI(SO4) 2- Zi'OSOs 21-120 and thereafter immersing the articles in an aqueous solution at approximately boiling tem--' perature' in which thesoluteconsists of about 0.l-to 1% of Zi(-SO2;)2---ZrOSO3-2H20 and about l to 6% of potassium permanganate.

' 12. The method of treating. magnesium, and magnesium base alloy articles to increase their resistance to corrosiom whi'ch comprises immersing the articles in an aqueous solution at approxi mately room temperature in which the solute consists of about 0.1 to 1% of manganese sulphate, and thereafter immersing the articles in an aqueous solution at approximately boiling temperature in which the solute comprises primarily about 0.1 to 1% aluminum sulphate and about 1 to 6 of potassium permanganate, said solutions being effective to increase the resistance of said articles to corrosion.

I3. The method of treating magnesium and magnesium base alloy articles to increase their resistance to corrosion, which comprises im-- mersing the articles in a boiling aqueous solution 8 in whichthe solute consists" of about 0.1 to1-% of a salt of a metal which is below magnesium in the eieetmmotwe serie and the'rea fter immersing the article's in a boiling aqueous solution in' the solute coniprise's primarily about 0.1 to 1% of a salt of ainetal whicl ris below magnesium inthe electroihotive' se'i 'ies and about i to 6% ot a night y oxidizing alk ali- Instalsa'lt selected from the group consisting ofwater soluble ermanganates and dichi ofriate's; saidsolutions being fie'ctive to increase the resistance" of said articles to corrosion.

RENE GIDE.

REFERENCES GHED The following references are of recordinthe file of this patent-5 STATES" PATENTS Number Name Date 1,710,143 Pacz Apr. 30; 1929 1,965,269 Tosterud' -l s July 3, 1934 1,971,240 Tosterud' Aug. 21', 1934' 2,2l9g554 Batcheller Oct. 29, 1940 seamen Percuss- Number 7 Country M Date M 510,353 Great Britain l- --e- July 24, 1939 Certificate of Correction Patent No. 2,512,493 June 20, 1950 RENE GIDE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 32, for the word solution read solutions;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of September, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Oowwm'ssz'oner of Patents. 

5. THE METHOD OF TREATING MAGNESIUM AND MAGNESIUM BASE ALLOY ARTICLES TO INCREASE THEIR RESISTANCE TO CORRESION, WHICH COMPRISES IMMERSING THE ARTICLES IN AN AQUEOUS SOLUTION IN WHICH THE SOLUTE CONSISTS OF ABOUT 0.1 TO 1% OF A SALT OF A METAL WHICH IS BELOW MAGNESIUM IN THE ELECTROMOTIVE SERIES, AND THEREAFTER IMMERSING THE ARTICLES IN A BOILING AQUEOUS SOLUTION IN WHICH THE SOLUTE COMPRISES PRIMARILY ABOUT 1 TO 6% OF POTASSIUM PERMANGANATE, SAID SOLUTIONS BEING EFFECTIVE TO INCREASE THE RESISTANCE OF SAID ARTICLES TO CORROSION. 